Geographical distribution of helium isotope ratios in northeastern Japan

In order to study the precise geographical distribution of helium isotope ratios in northeastern Japan and compare it with geophysical data, we collected 43 gas and water samples from hot and mineral springs in the region where the ratio had never been reported, and measured the ³He/⁴He and ⁴He/²⁰Ne ratios of these samples. It was found that the ³He/⁴He ratios show clear contrasts between the forearc and the back-arc regions in the Tohoku district in northeastern Japan. In the forearc region, the ratios are smaller than 1 R_A (1 R_A = 1.4 × 10⁻⁶; R_A means the ³He/⁴He ratio of the atmosphere). On the other hand, those along the volcanic front and in the back-arc region are apparently higher. Moreover, we found a variation in the ³He/⁴He ratios along the volcanic front. In Miyagi Prefecture (38–39°N), the ratios range from 2 to 5 R_A. On the other hand, the ratios are less than 1 R_A in and around the southern border between Iwate and Akita Prefectures (39–39.5°N). Comparing the distribution of helium isotope ratios to results of recent geophysical studies, we found that the features in geographical distribution of helium isotope ratios are similar to those of seismic low-velocity zone distributions and high Qp⁻¹ distributions in the uppermost mantle. These observations strongly suggest that the helium isotope ratios reflect the distribution of melts in the uppermost mantle and are a useful tool for investigating the origin, behavior, and distribution of deep fluids and melts.     

Holocene millennial-scale climate variations documented by multiple lake-level proxies in sediment cores from Hurleg Lake,Northwest China

Millennial-scale climate variability has not been well documented in arid northwest China due to the scarcity of high-resolution, well-dated paleoclimate records. Here we present multi-proxy records from sediment cores taken in freshwater Hurleg Lake on the northeastern Tibetan Plateau, which reveal millennial-scale lake-level and climate variations over the past 8,000 years. This high-elevation region is very sensitive to large-scale climate change, thus allowing us to better understand Holocene climate variations in East Asia. The lake-level record, derived from lithology, magnetic mineralogy, carbonate isotopes, ostracode shell isotopes and trace elements, X-ray fluorescence (XRF), and gray scale data, indicates a highly variable and generally dry climate from 7.8 to 1 ka (1 ka = 1,000 cal year BP), and a relatively stable and wet climate after 1 ka. Superimposed on this general trend, six dry intervals at 7.6–7.2 ka, 6.2–5.9 ka, 5.3–4.9 ka, 4.4–3.8 ka, 2.7–2.4 ka, and 1.7–1.1 ka were detected from the high-resolution carbonate content and XRF data. The generally dry climate between 7.8 and 1 ka was almost synchronous with the decrease of East Asian and Indian monsoon intensities shortly after 8 ka. The six dry intervals can be correlated with weak monsoon events recorded in the East Asia and Indian monsoon regions, as well as the North Atlantic cold events. Our data suggest that millennial-scale monsoon variations could cause highly variable climate conditions in arid northwest China during the Holocene. These millennial-scale climate variations may reflect changes in solar variation and/or changes in oceanic and atmospheric circulation.     

HFSE-rich picritic rocks from the Mino accretionary complex,southwestern Japan

Sills, pillow lavas and hyaloclastites of the HFSE-rich picrite and related rocks (ankaramite and basanite) occur in the Middle Permian cherts in the Mino Jurassic accretionary complex, southwestern Japan. These rocks show systematic trace element patterns enriched in incompatible elements, which indicate that the associated ankaramite and basanite are formed by the crystal fractionation from the picrite. The presence of the hyaloclastite in the chert sequence covering a large tholeiitic greenstone body indicates that the picrite was produced in an intraoceanic setting in the Middle Permian time subsequent to the extrusion of the voluminous oceanic island tholeiite. The Mino picrites resemble the Siberian meimechite and Polynesian picrites in its HFSE-rich chemical composition. The HFSE enrichment in these picrites cannot be explained by low degree of partial melting of primitive peridotite mantle only, and needs a source material involving recycled oceanic crust (eclogite). The differences in MgO content and in TiO₂/Al₂O₃ and Zr/Y ratios among the HFSE-rich picrites indicate that the melting pressure increases from the Polynesian picrite through Mino picrite to Siberian picrite. This may reflect the increasing thickness of the overlying lithosphere at the time and place of magmatism. The HFSE-rich picrites may be a product of a superplume event. The presence of HFSE-rich picrite in Mino and Siberia indicate that the superplume activities occur in both continental and oceanic settings in the Permian time.     

Diurnal variations in streamflow and water quality during the summer dry season

In a headwater basin covered with boreal forest in northern Japan, the summer dry flow was monitored each summer from 1985 to 1993. Streamflow and specific electrical conductance fluctuated diurnally and these variations were attributed to daytime evapotranspiration. In 1989, the daytime reduction in streamflow and conductance were accompanied by a reduction in the HCO^?₃ concentration. The low flow hydrograph was separated into two components using HCO^?₃ and Cl^? concentrations in August 1989, assuming low flow to be a mixture of delayed subsurface flow and of quick shallow flow. The slight diurnal variation in the ratio of shallow flow to subsurface flow caused the diurnal variation in conductance by changing the HCO^?₃ concentration.     

10th annual report on the international status of engineering geology—year 2004-2005; encompassing hydrogeology, environmental geology and the applied geosciences

The year was particularly eventful in terms of the recognition of improved technologies impinging on the duties of the Engineering Geologist. National economies were strained to the limit under the pressure of the new world terrorist attacks and burgeoning populations. much of which stemmed from escapes from oppressive national regimes to the free world. The impacts of terrorism range from increased danger and costs of field work, to special design considerations and postponed and delayed project work.On the positive side, continued progress has been made in the means of recognition and professional development of our practitioners and in the general call for their work. Competent engineering geologists are in consistent demand, but the working conditions are not improved. A general deterioration of university funding, aggravated by bureaucratic excesses among administrators, have tended to make life miserable for dedicated faculty and a general move is afoot to cut back on the number of funded geology departments in North America and Europe. This situation has also been worsened by the general withdrawal of the mineral industries and by retraction of the petroleum companies from all but their most favored campuses.     

Semi-brittle behavior of wet olivine aggregates: the role of aqueous fluid in faulting at upper mantle pressures

The role of aqueous fluid in fracturing in subducting slabs was investigated through a series of deformation experiments on dunite that was undersaturated (i.e., fluid-free) or saturated with water (i.e., aqueous-fluid bearing) at pressures of 1.0–1.8 GPa and temperatures of 670–1250 K, corresponding to the conditions of the shallower regions of the double seismic zone in slabs. In situ X-ray diffraction, radiography, and acoustic emissions (AEs) monitoring demonstrated that semi-brittle flow associated with AEs was dominant and the creep/failure strength of dunite was insensitive to the dissolved water content in olivine. In contrast, aqueous fluid drastically decreased the creep/failure strength of dunite (up to ~?1 GPa of weakening) over a wide range of temperatures in the semi-brittle regime. Weakening of the dunite by the aqueous fluid resulted in the reduction of the number of AE events (i.e., suppression of microcracking) and shortening of time to failure. The AE hypocenters were located at the margin of the deforming sample while the interior of the faulted sample was aseismic (i.e., aseismic semi-brittle flow) under water-saturated conditions. A faulting (slip rate of ~?10^?3 to 10^?4 s^?1) associated with a large drop of stress (Δσ?~?0.5 to 1 GPa) and/or pressure (ΔP?~?0.5 GPa) was dominant in fluid-free dunite, while a slow faulting (slip rate?<?8?×?10^?5 s^?1) without any stress/pressure drop was common in water-saturated dunite. Aseismic semi-brittle flow may mimic silent ductile flow under water-saturated conditions in subducting slabs.     

Effectiveness of superelastic bars for seismic rehabilitation of clay‐unit masonry walls

This paper presents the results on shaking table tests of half‐scale brick walls performed to investigate the effectiveness of newly developed Cu–Al–Mn superelastic alloy (SEA) bars in retrofitting of historical masonry constructions. Problems associated with conventional steel reinforcing bars lie in degradation of stiffness and strength, or pinching phenomena, under cyclic loading, and presence of large residual cracks in structures during and after intense earthquakes. This paper attempts to resolve the problems by applying newly developed Cu–Al–Mn SEA bars, characterized by large recovery strain, low material cost, and high machinability, as partial replacements for steel bars. Sets of unreinforced, steel reinforced, and SEA‐reinforced specimens are subjected to scaled earthquake excitations in out‐of‐plane direction. Whereas steel‐reinforced specimens showed large residual inclinations, SEA‐reinforced specimens resulted in stable rocking response with slight residual inclinations. Corresponding nonlinear finite element (FE) models are developed to simulate the experimental observations. The FE models are further used to examine the sensitivity of the response with respect to the variations in experimental conditions. Both the experimental and numerical results demonstrate the superiority of Cu–Al–Mn SEA bars to conventional steel reinforcing bars in avoiding pinching phenomena. Copyright © 2012 John Wiley & Sons, Ltd.